1. Field of the Invention
This disclosure relates to a method of fabricating an organic light emitting diode display.
2. Discussion of the Related Art
Recently, various flat panel display devices are being developed to reduce weight and volume, the shortcomings of the existing cathode ray tubes (CRTs). Such flat panel display device includes a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an electroluminescence (EL) device, and the like.
The PDP receives much attention as a display device because its fabrication process is simple and it is so light, thin, short, and small as to be most favored to secure a large scale screen, but has shortcomings in that its luminous efficiency and luminance are low and it consumes much power. A thin film transistor (TFT) LCD is one of the most commonly used flat panel display devices, but with a problem in that its viewing angle is narrow and response speed is low. The EL device is divided into an inorganic light emitting diode display device and an organic light emitting diode display device according to a material of a light emission layer. Among them, the organic light emitting diode display device, a self-emission device, has advantages of fast response speed and high luminous efficiency and luminance, and a wide viewing angle.
The organic light emitting diode display device has an organic light emitting diode (OLED) as shown in FIG. 1.
The OLED includes an organic compound layer, and cathode and anode electrode facing each other with the organic compound layer interposed therebetween. The organic compound layer is formed as a multi-layer by stacking an electron injection layer (EIL), an electron transport layer (ETL), an emission layer (EML), a hole transport layer (HTL), and a hole injection layer (HIL). When a driving voltage is applied to the anode and cathode electrodes, holes which have passed through the HTL and electrons which have passed through the ETL are moved to the EML to form exciters to resultantly make the EML emit visible light.
In the related art OLED display device, the EML is formed through a thermal evaporation method as shown in FIG. 2. To perform the thermal evaporation method, a boat 30 that houses EML materials for R, G, and B, and a metal mask 20 for inducing the EML materials transferred from the resistance-heated boat 30 such that they are deposited at a corresponding position are required, the metal mask 20, supported by a mask frame 25, is aligned on a substrate 10 with a thin film transistor (TFT) array 15 formed thereon. In the related art OLED display device, the R, G, and B EMLs are deposited by changing the alignment position of the metal mask 20.
Such related art OLED display device fabrication method has the following problems.
First, in the related art method, the size of the metal mask is determined according to the size of a substrate. As the substrate is increased in size, the size of the metal mask is bound to be increased. As the size of the metal mask increases, the mask is increasingly bent. Thus, in the related art deposition method using the metal mask, it is difficult to precisely pattern a light emission layer, failing to cope with a large area and high definition.
Second, in the related art method, the board holding the light emission materials is separated by a certain distance from a substrate and heated, and then, the light emission materials are deposited on the substrate, which results in lengthening of a process total accumulated time (TACT) in forming a light emission layer. As the substrate is increased in size, the distance (D) between the substrate and the boat is bound to be increased to secure uniformity of the light emission layer deposited on the substrate, leading to an increase in the size of a chamber used for forming the light emission layer.